Effects Of Nitrogen Deposition On Soil Nitrogen Mineralization In Urban-Rural Forests

Soil nitrogen mineralization regulates soil nitrogen availability and affects the absorption and utilization of nitrogen by plant roots.Its turnover efficiency is a key factor limiting plant nutrient uptake and land productivity improvement.Long-term nitrogen deposition can change soil nutrient status and microbial community structure,and affect soil nitrogen mineralization.At present,China’s urbanization process is in a stage of accelerated development,which has direct and indirect impacts on the structure and function of forest ecosystems around urban areas,and leads to significant changes in many ecological environment factors.Therefore,the effects of nitrogen deposition on nitrogen mineralization in urban-rural forest soils may be different.In order to provide a scientific basis for the nitrogen cycle process of urban-rural forest under nitrogen deposition,in this study,the in-situ mineralization experiments of soil nitrogen under simulated nitrogen deposition(0,50and 100 kg N·ha^-1·yr^-1)were carried out in suburban and rural forest plots in Anhui Province.The seasonal and interannual changes of soil nitrogen mineralization in suburban and rural forests were studied,and the differences of soil nitrogen mineralization under nitrogen deposition in different seasons,years,soil layers,treatments and locations were analyzed.The main conclusions are as follows:（1）From the perspective of seasonal dynamics,the soil inorganic nitrogen pools（ammonium nitrogen,nitrate nitrogen and inorganic nitrogen）in suburban and rural forests under nitrogen deposition were generally high at the end of the growing season and low at the end of the growing season,and the seasonal dynamic changes of rural forests fluctuated greatly.The seasonal dynamics of soil net nitrogen mineralization rate（net ammonification,nitrification and mineralization rate）in suburban forests under nitrogen deposition mainly showed a“bimodal curve”,while that in rural forests showed a“unimodal curve”.（2）From the perspective of interannual dynamics,in the first year of simulated nitrogen deposition,nitrogen deposition inhibited the mineralization rate of nitrate nitrogen,inorganic nitrogen and net nitrogen in suburban forest soil.It mainly promoted the content of inorganic nitrogen pool and net nitrogen mineralization rate in rural forest soil.In the fifth year of simulated nitrogen deposition,nitrogen deposition promoted the inorganic nitrogen pool and net nitrogen mineralization rate of suburban forest soil.Nitrogen deposition promoted the content of inorganic nitrogen pool in rural forest soil and inhibited the net nitrogen mineralization rate of soil.（3）In the vertical distribution,the content of soil inorganic nitrogen pool in 0-10 cm soil layer of suburban and rural forest soil under nitrogen deposition was higher than that in 10-30 cm soil layer.The net nitrogen mineralization rate of 0-10 cm soil layer in suburban forest was higher than that of 10-30 cm soil layer,and the net nitrogen mineralization rate of 0-10cm and 10-30 cm soil layer in rural forest were similar.（4）All nitrogen deposition treatments can effectively improve the nitrogen availability of urban-rural forest soil.Comprehensive analysis showed that the nitrogen deposition of urban-rural forest was 50 kg N·ha^-1·yr^-1 to promote soil nitrogen mineralization,and the soil nitrogen availability was the best,thus providing sufficient nitrogen for vegetation to be directly absorbed and utilized,which was conducive to creating beautiful,stable and sustainable urban-rural landscaping space.In summary,the effects of nitrogen deposition on nitrogen mineralization in urban-rural forest soils are different.This study provides a scientific basis for improving the theory of nitrogen cycle in forest ecosystems,and provides technical support for soil improvement in green space during regional urbanization.